Option variable
expopDefault value: 0
expop is the highest positive exponent which is
automatically expanded. Thus (x + 1)^3, when typed, will be
automatically expanded only if expop is greater than or equal to 3.
If it is desired to have (x + 1)^n expanded where n is greater than
expop then executing expand ((x + 1)^n) will work only if maxposex is
not less than n.